Oxidation inhibitor for lubricating oils



Sept 2, 1952 c.' E. sAUNDERs ETAL 2,609,343

OXIDATION INHIBTOR FOR LUBRICATING OILS Filed July l2, 1948 R. m.. new D wNP M d NUR 45N EAU R VSM O m .1. EM A SS EE .LL RR AA HH CC Y B Patented Sept. 2, 1952 I, Charles E. Saunders and CharlesMQMurphy;Jr., Y u

' Washington, D. C.

Application July 12, 1948, serial No. 33,196l Ysolaims. (o1. 25a-46.3)y (Grantedunder the act of` March 3, 1883, Vas,

w amended April 30, 192835-370 O.,G. 757;);

This invention relates to oxidation inhibitor additives used with lubricating oils. It relates particularly tosuch additives used with the relatively new synthetic diester type of lubricating The prior art of inhibitor additives for lubricants is extensive and includes other types of inhibitors besides those directed specically toward the protectionl of the lubricant itself from oxidation, with which the present invention is concerned.

There are many aspects to the problem of lubricant oxidation. For example, considerable variation is found in the products formed upon oxidation of diierentlubricants, and their eiect on diii'erent types of lubricated systems. Thus, it isnot surprising that a very large number of oxidation-inhibitor additives have been suggested and are in use. These additives fall largely into general groups consisting of aromatic phenolic compounds, aromatic amines, organic sulfur compounds and organometallic compounds.

Most Yadditives were developed for and are now used in (natural occurring) petroleum type oils which have been refined by solvent-treating processes. It is well established that petroleum oils in their natural state contain certain natural oxidation-inhibitors, and that unfortunately thesejarepartially removed by rening operations, particularly solvent-treating processes. However, itis also known that ordinary solventrening does not entirely remove these natural inhibitors, and their presence even in small amounts, distinguishes the petroleum oils from the new synthetic oils. And as would be expected, the synthetic oils, though superior in many .propertiesl are deiinitely inferior to petroleum oils with respect to stability toward oxidation.

It is the general object of this invention to provide a lubricating oil having a high resistance to oxidation.

Another object is to provide suchan oil in which the oxidation-inhibitor additive is an inexpensive and readily available chemical com` where X` is an element'selectedfrom thegroup, sulfur, selenium'and-tellurium, and R isz'either hydrogen or an.;alkyl: radicahqor hydrogen in some positionsjandone-*or more alkyl radicals inothers. "The terms commonlyused in the art to designa-te.` these compounds are n fphenothazine, phenoselenazine and phenotellurazine, according to the appropriate specific designation of X. The configuration shown is of the paratype, vthe hetero-atoms being in the para-(1', 4) relationship to each other.

y The invention includes the metaand orthoconfigurations also, typical structures of which` are:

The f'symbo'ls R and X have the same meanings as above.A v

The accompanying data are presented to il-v lustrate the effectiveness of the inhibitors in several-'species of diester oils.' The data vrepresent results of two types of experiments, viz', 'laboratory testsIand engi-ne-runssf.

The results of thelaboratory dynamic oxidation tests are given in the Vaccompanying data sheet.,v The test comprises aerating a 25 gram samplewith 201ml. of air per minute for 168' hoursfin-'the'pres'ence of copperfsteel and aluminum specimens. In thesetests several diier-I entfty'pes of `oils in one or more viscosity grades were employed for investigation 'of the eect of the inhibitor. The criteria for the degrees of oxidation occurring in these tests are changes in viscosity and neutralization number, and volatile-acid number.v Nel. itralizationA number, as used in this specification is definedin A.. S. T. M. designation: D188-27T. Volatile acid number is a test devised by ourselves whereby theatmos-U phere of the oxidation cell is continuously conducted through a standard solution of KOI-I during the run and the extent of neutralization of said solution is determined at the end of the run by back-titration. The results are reported ron the same basis as that of .neutralization number. vzperf gram of o il. We findthat the beginningwof i lformation of volatile Vacids `@frequently corresponds closely withy the end of the induction period for oxidation;

The importance of carrying out tests in the presence of metallic specimens is greater than is immediately apparent. 'I'his is because the products formed by action of the oxidation produced acids upon metals may actually catalyze further oxidation ofthe lubricant. Thus some additives :which are effective inhibitors of oxidation (as measured' by oxygen absorption, e. g.) when tested in glass, are complete failures when tested in metals. As is seen from boththe laboratory data and the engine test'runs, thelubricants embodying the present invention are very eiectlve in inhibiting oxidation in all its Jaspectsxl.-

Given below are the results of long-run engine tests on two oils, With and Withoutthegpresencejicj of a small quantity of inhibitor. The tests were. made with a 21A; horsepower Onan lil-LS gasoline engine operating under a-.full-loada`tr 1800A R. P. M. Samples were taken before ther-unand after various periods of time.`

The'atableimmediatelyzbelow shows the effect onoxidation, as measured by neutralization num. ber, o-f0;2'% phenothiazine added to the diester oil, di-l1'2(2-rnethylpropyl)4ethyloctyl]- Seba-fcate.- Iny this specicationwe conveniently refer' tothisicompound as tetradecyl sebacate.

Neutralization Number Hours Run inhibited uninhibiied The Cl'ankcase temperature was approximately 150 F. The oil capacity of the engine was 21A quarts and the oil consumption was about 2 mL/hr. forthe inhibited oil and about 4 m1./hr. for the uninhibited. After 286 hours, the engine ruimingv Withzthe uninhibitedoil stopped due to the extremely bad condition of the lubricant.y The piston rings and pin were stuck. Theinterior. parts-of the engine; Were-.all` badly var:` nished.` vWith the inhibitedvoil the engine Wasstill running after 500 hours andthe partswere in good condition. The viscosity of both oils'was. substantially unchanged during the tests.

The .following table shows the eilect of the inhibitor. with di (Z-ethylhexyl)v sebacate, ari--Y other diester-` oil. The test conditions were sim- A ilar togthose above and oxidation was measured on the:- basisf of neutralization number and precipitation number. This latterl test determines the quantity of naphtha-,insoluble material pres.- enj'l aftergoxidationiand isldescribed in 4A. S.. T, designation: 091:40;

Neutralization Number vPrecipitationv Number Hours Run l inhibited l y @inhibited inhibited ininhibiiefi The crankcase temperature was about F. The-oil consumption Wassabout 9 inl/hr. for the inhibited oil and, about 11 ml./hr. forthe unin` hibited oil. In this case bothengines-Wererunf 7o.

ning after 300 hours, but theexhaust valve of that running on the uninhibitedf oil Wassticking and the piston pin was tight. The Aengine and lubricant, in the inhibited oil test were both in good 4condition,after 300r hours.

'Airurther example of alkyl esters of organic dicarboxylic acids is undecyl adipate. A 'The foregoing `examples are intended to be iilustrative only and not limitative except as de- .nedgby the;herewith appended claims.

l. Acomposition of matter comprising an alkyl diester ofan organic dicarboxylic acid andan oxidation-inhibiting amount offa compound se lected from the group consisting of Vphenothiazine, phenoselenazine, and .phenotellurazine.`

2. A composition of mattercomprising an alkyl; diester of an organic dicarboxylic acid' and an,

oxidation-inhibiting amount of a compoundihav-- ing the general formula:

whereX is anfelement sele'cted'from the group consisting of;sulfur,v selenium vor tellurium,land` Rfrepresentsa'member selected from the group consisting of hydrogen andalkyl radicals.

3. A composition of matter comprisingwthe'diester oil, tetradecyl sebacate, and an oxidation-v inhibiting Yamount of ja compound selected vfrom the group consisting ofv phenothiazine, phenoselenazine andpheno-tellurazine. Y

V1i. A composition of matter comprising the diester oil, di(2ethylhexyl) sebacataand an oxdation-inhibiting amount of a compound selected from the group consisting otf phenothiazine, phenoselenazine and phenotellurazine.

5. A composition of matter comprising the 'di esteroil, undecyl aldipate, andan oxidation-einhib'iting amount cfa compound selectedfrom the group consisting of phenothiazine, phenoselen-f azine and phenotellurazine.l

CHARLES E. sAUNDERis. CHARLES M. JR.

REFERENCES CITED The'following references are of record in 'the' file of this patent:

I UNITED STATES PATENTS Number Name Date 2,190,648 Cantrell Feb. 20. 1940 2,220jl'23 Lewis i ,Nov. 5, 1940 2,417,281v 'Wasson Mar.z1l,1947. 2,466,647` Stern Y Apr. 5, 19494 OTHER iRtEF'ERllNCES4k V No. 77, June 16-20, 194?. pps. 2l and- 22.

`.symposium on Synthetic Lubricants, Amer. Soc. forTesting Materialsf? Specia1 Tech; .Rubia 

1. IN A COMPOSITION OF MATTER COMPRISING AN ALKYL DIESTER OF AN ORGANIC DICARBOXYLIC ACID AND AN OXIDATION-INHIBITING AMOUNT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF PHENOTHIAZINE, PHENOSELENAZINE, AND PHENOTELLURAZINE. 